1. Field of the Invention
The present invention relates to a glaucoma diagnosis apparatus suited for use in diagnosing glaucoma.
2. Prior Art
In the field of medical ophthalmology, glaucoma is known as a disease resulting from excavation or deficiency in the nerve fiber layers as caused by increased intraocular pressure, among others. At an advanced stage, glaucoma causes irreversible vision disorder, leading to loss of sight. Therefore, early discovery of signs of glaucoma is regarded as an urgent task. However, the nerve fiber layers vary in thickness from portion to portion on the ocular fundus and the progress of the defect of the nerve fiber layers is generally gradual until the morbid condition becomes severe, so that even when the fundus image is available as a result of ophthalmography of the fundus of a patient at an early symptom stage, it is difficult for an oculist to judge, based on that image, whether there is a defective area in the nerve fiber layers.
Meanwhile, it is known that the nerve fiber layers are a birefringent substance showing different refractive indices according to the direction of vibration (polarization) of light.
Thus, when the nerve fiber layers are irradiated with a polarized laser beam, the polarized light components pass through that layer at different velocities, resulting in different times for passing through the nerve fiber layer for each of the components of the polarized laser beam (phase difference).
The magnitude of this phase difference is positively correlated with the thickness of the nerve fiber layers at the portion through which the light has passed.
The polarized light is classified simply into linearly polarized light, circularly polarized light and elliptically polarized light according to the quantity of phase difference between the polarized light components.
Utilizing this fact, a glaucoma diagnosis apparatus has been developed which converts a laser beam from a laser diode to the linearly polarized state by means of a polarizing filter having linearly polarizing characteristics, modulates this laser beam to circularly polarized light using a quarter wavelength plate, deflects that laser beam by means of a scanning unit to scan the ocular fundus therewith, detects the rate of change in phase difference of the light reflected from the ocular fundus and determines the thickness of the nerve fiber layers.
However, this glaucoma diagnosis apparatus in the prior art can only scan a certain narrow area of the ocular fundus and cannot examine a wide area at a time. It has another problem that the data cannot be obtained as image information.
A further problem is that such a glaucoma diagnosis apparatus tends to be expensive and is still hardly available for ordinary ophthalmologists.
Accordingly, it is an object of the present invention, which has been made in view of the limitations of the related art discussed above, to provide a glaucoma diagnosis apparatus capable of determining the thickness of the nerve fiber layers in a simple, easy, and inexpensive manner by improving the optical system of a currently existing retinal or fundus camera in common use.
The glaucoma diagnosis apparatus according to one aspect of the invention comprises an illuminating optical system for illuminating the ocular fundus of a subject to be examined with circularly polarized illuminating light and an imaging optical system including a CCD camera for photographing the image of an ocular fundus based on the reflected illuminating light from said fundus, characterized in that said CCD camera has a polarizing filter provided integrally with the imaging surface of said CCD camera and said filter is composed of repetitions of a unit platelet being a couple of polarizing microplates one of which transmits one of said linearly polarized light components crossing with each other of said reflected illuminating light and another adjacent polarizing microplate which transmits linearly polarized light components whose direction is crossing to both of said linearly polarized light components of the reflected illuminating light. It is desirable that this glaucoma diagnosis apparatus comprises an illuminating optical system for illuminating the ocular fundus of a subject to be examined with circularly polarized illuminating light and an imaging optical system including a CCD camera for photographing the image of an ocular fundus based on the reflected illuminating light from said fundus, characterized in that said CCD camera has a polarizing filter provided integrally with the imaging surface of said CCD camera and said filter is composed of repetitions of a unit platelet being a couple of polarizing microplates one of which resolves one of said linearly polarized light components crossing with each other of said reflected illuminating light and another adjacent polarizing microplate which resolves said reflected illuminating light into linearly polarized light components crossing orthogonally with each other and adjacent polarizing microplates resolving the above reflected illuminating light into linearly polarized light components crossing with both of said linearly polarized light components mentioned above.
The glaucoma diagnosis apparatus defined in the above aspect of the invention is further provided in that said linearly polarized light component which is crossing to both of said linearly polarized light components is in the direction of 45xc2x0 relative to both of said linearly polarized light components, and each polarizing microplate corresponds to each pixel of said CCD camera.
The glaucoma diagnosis apparatus according to another aspect of present invention comprises an illuminating optical system for illuminating the ocular fundus of a subject to be examined with circularly polarized illuminating light and an imaging optical system including a CCD camera for photographing the image of an ocular fundus based on the reflected illuminating light from said fundus, characterized in that the imaging optical system is provided at a position conjugated with the imaging surface of said CCD camera with a polarizing filter composed of repetitions of a unit platelet being a couple of polarizing microplates one of which resolves said reflected illuminating light into linearly polarized light components crossing diagonally with each other and another polarizing microplate which resolves said reflected illuminating light into linearly polarized light component having a direction crossing with both of said linearly polarized light components.
The glaucoma diagnosis apparatus defined in the above aspect is further provided in that the linearly polarized light component in the direction crossing with both of the above-mentioned linearly polarized light components is in the direction of 45xc2x0 relative to both of the above linearly polarized light components and that each polarizing microplate corresponds to a pixel of the CCD camera.
The glaucoma diagnosis apparatus defined in the above aspect is more further provided in that a shape of elliptically polarized light is computed based on magnitude of the output of each pixel corresponding to each polarizing microplate constituting said unit platelet and thickness of the nerve fiber layers of said ocular fundus is determined based on said shape of the elliptically polarized light.
The glaucoma diagnosis apparatus defined in the above aspect is further provided in that said polarizing filter is arranged insertably into and retractably from the optical path of said imaging optical system.
The glaucoma diagnosis apparatus according to other aspect of the present invention comprises an illuminating optical system for illuminating the ocular fundus of a subject to be examined with circularly polarized illuminating light and an imaging optical system for photographing the image of an ocular fundus based on the reflected illuminating light from said fundus, characterized in that said imaging optical system is provided with a resolving optical system which resolves said reflected illuminating light into linearly polarized light components crossing diagonally with each other and another resolving optical system which resolves said reflected illuminating light into linearly polarized light component having a direction crossing with both of said linearly polarized light components, and each resolving optical system is provided with a CCD camera for photographing the fundus image based on the reflected illuminating light resolved into the respective linearly polarized light components.
The glaucoma diagnosis apparatus defined in the above aspect of the invention is further provided in that the direction of said linearly polarized light component which is crossing to both of said linearly polarized light components is in the direction of 45xc2x0 relative to both of said linearly polarized light components.
The glaucoma diagnosis apparatus in accordance with further aspect of the invention comprises an illuminating optical system for illuminating the ocular fundus of a subject to be examined with circularly polarized illuminating light and an imaging optical system including a CCD camera for photographing the image of an ocular fundus based on the reflected illuminating light from said fundus, characterized in that the imaging optical system is provided with a rotatable polarizing filter which transmits linearly polarized light components of said reflected illuminating light.
The glaucoma diagnosis apparatus defined in the above aspect of the invention is further provided in that a green filter for transmitting green light is provided in the above-mentioned illuminating optical system.
By using the glaucoma diagnosis apparatus defined in one of the above aspects of the invention, it is possible to measure the thickness of the nerve fiber layers by improving the optical system of an existing fundus camera.